The invention concerns a bounce-free lifting device, preferably for semi-conductor wafers in automatic wafer probes, which allows attaining a rapid lifting movement in sensitive systems.
GDR Letters Patent WP 101 783 describes a lifting device for rapid and bounce-free contacting, where the armature is held in two Belleville springs which, by having a steeper load-deflection line, will act with their spring effect against the force-travel line of the electromagnet. The spring constant is adjustable herein by variable initial tensioning. This lifting device is limited in its application to relatively small forces, i.e., with large semi-conductor wafers it is not possible to realize short operating times. The reasons herefor can be found in the large counteracting force of the progressively acting spring and the thus resulting high power requirement of the solenoid coil.
In the U.S. Pat. No. 3,936,743, a gripper head is described which realizes the lifting movement by means of an eccentric driven by a step motor. Herein, the friction between individual parts is of disadvantage as it also causes mechanical wear at these parts.
It is also of disadvantage that the gripping head consists of several individual parts and that exact parallel guiding of the holding surface in the operating position is difficult.